The open-mid back rounded vowel, or low-mid back rounded vowel,[1] is a type of vowel sound, used in some spokenlanguages. The symbol in the International Phonetic Alphabet that represents this sound is ⟨ɔ⟩. The IPA symbol is a turned letter c and both the symbol and the sound are commonly called "open-o". The name open-o represents the sound, in that it is like the sound represented by ⟨o⟩, the close-mid back rounded vowel, except it is more open. It also represents the symbol, which can be remembered as an o which has been "opened" by removing part of the closed circular shape.

Its vowel backness is back, which means the tongue is positioned as far back as possible in the mouth without creating a constriction that would be classified as a consonant. Unrounded back vowels tend to be centralized, which means that often they are in fact near-back.

Its roundedness is protruded, which means that the corners of the lips are drawn together, and the inner surfaces exposed.

Mainly in speakers without the cot–caught merger. It may be lower [ɒ]. (It is rarely lowered to /ɒ/ in before liquids/l ɹ/, and may thus be more familiar to many North Americans in r-colored form, /ɔ˞/.)

^Wikström (2013:45), "It seems to be the case that younger RP or near-RP speakers typically use a closer quality, possibly approaching Cardinal 6 considering that the quality appears to be roughly intermediate between that used by older speakers for the LOT vowel and that used for the THOUGHT vowel, while older speakers use a more open quality, between Cardinal Vowels 13 and 6."